The present invention relates generally to power door lock circuits for vehicles. More particularly, the invention relates to a circuit which responds to the presence of the ignition key in the ignition and also to an open vehicle door, by disabling the power door lock mechanism and causing the vehicle horn to sound when the door lock actuator is pressed.
Power door locks are a popular accessory on automotive vehicles. Although there is some variance in the manner in which power door lock mechanisms are implemented, most power door locks employ motors which lock the vehicle doors when energized by one polarity and which unlock the vehicle doors when energized by the opposite polarity. The locking motors or mechanisms are typically responsive to some form of actuator, such as a push button switch or rocker switch, which applies a voltage of the proper polarity across the lock motors to cause them to lock or unlock the associated doors.
Undoubtedly few have escaped the inconvenience and embarrassment of accidentally locking one's keys in the car. Addressing this problem, most automotive vehicle manufacturers provide some form of audible warning or alarm system, typically in the form of a buzzer, chime or synthesized voice. The conventional audible alarm senses when the ignition key is left in the ignition and the door (usually the driver's door) is opened. While serving as a useful reminder, some people lock their vehicle doors so automatically, that the audible warning alarm may not be effective, particularly in noisy surroundings in which the alarm may be unheard.
The above problem is even more acute in vehicles equipped with power door locks. Power door locks allow all vehicle doors to be locked at once. Should the driver accidentally leave the keys in the ignition, step out of the vehicle and depress the power door lock actuator, the chances of being locked out of the car are very great, since all doors are mechanically assured to be locked.
To overcome this problem, it has been proposed to provide a logic circuit for providing a warning independent of the audible warning alarm, although such alternative warning systems have proven to be unduly complicated and hence too expensive to be suitable for mass production in the comparatively competitive automobile industry.